Surgery is always looking for the most minimal invasion to deep targeted regions. Preformed passageways are always beckoning the surgeon to be used. In one example situation the nasal passages can be used to access diverse regions as skull base, orbit, medial temporal bone, C1 and C2 of the cervical spine, the paranasal sinuses and obviously structures normal to and pathologic in the nasal passages itself. Common to all of these approaches is a long narrow traverse to reach tissues that are often small and adjacent to critical structures such as the eye, brain and spinal cord.
Surgery to this type of region is usually done with one operator working at a time. One hand holds an endoscope for visualization and the other for the operating tool usually one tool for one action and traded out for the next. It is apparent that a fat, rigid, long tool is hard to use under these circumstances to the point of danger. Such is the situation with many of the sonic and ultrasonic devices now available.
For deep and narrow surgery many devices and techniques have been developed and used. For example, cold unpowered steel grasping cutting instrument or a rotating suction debrider such as marketed by Medtronics have been employed. The latter is an improvement as it removes tissue and resulting blood. As procedures are usually done with an endoscope any bleeding rapidly obscures any visualization of the surgical site. To surgically manipulate tissue (disintegrate, incise, elevate and dissect) and not obscure the surgical field with blood, instruments which apply various forms of energy have been developed. These energies include heat, cold (cryosurgery), radio frequency, laser light, plasma and sound. Energy driven surgical tools which apply acoustic energy to tissues can cause tissue effects deep in the body structures through relatively long, narrow passages. Each of these by itself has advantages and faults.
Ultrasonic devices on the market today are based on the “Langevin design” in which an in-line stack of piezo ceramic wafers are compressed between a proximal metal mass (blocking mass) and a metal condenser using a large bolt. The expansion and contraction of the piezo wafers is caused by large potentials across the ceramic wafers. The energy produced by the stack is blocked from proximal extension with a large mass and is received and condensed by the condenser at the distal end of the stack. Various waveguides are then attached to the condenser. Through these the energy thus flows from piezos to distal end. To achieve the best concentration of this sound energy the condenser and waveguide have to be of a length that achieves resonance. The greatest movement then is found at the antinode of the resonant action. The phakoemulsifier as described by Kelman is an example.
The CUSA (cavitron ultrasonic surgical aspirator) is used in brain surgery. Using the same Langevin design, a larger energy source and waveguide associated with a relatively thick walled suction tube is used for neurosurgical removal of brain tumors. The effects are on high water content brain tissue that is repeatedly crushed but not the collagen rich vascular walls. The crushing action produces tiny plugs of crushed tissue that is removed by an integrated suction. Thus disintegrating the tumor and removing the detritus.
Another surgical tool that uses ultrasound is a harmonic scalpel. A rapid longitudinal, reciprocating movement imparted into one jaw of a grasping instrument results in crushing, heating and coagulative destruction that cuts tissue and seals blood vessels. The associated heat generated causes coagulation. The cutting is very precise due to the high rate of movement and the narrow loss of cells in the kerf.
Other surgical instruments employ tissue welding and coagulation produced by sound energy reduced to heat as a waveguide transmits sonic energy to tissues. Blood vessels can be fused closed or various clips can be fused to clamp vessels.
In the early 1990s trials of the CUSA for intranasal surgery (polypectomy) were conducted. This tool was excellent at removing tissue almost bloodlessly but was exceedingly slow. Trial use of CUSA for tonsillectomy has also been published. The advantages were precise intracapsular excisions with little bleeding.
The SonoPet, based on the Langevin design, was introduced recently for otolaryngology work. In one embodiment it is a rigid straight hollow waveguide that suctions blood and detritus. It also is marketed with a variety of rasp tips for vibratory motion and bone abrading. From a nasal surgery standpoint, it can remove a polyp and abrade bone to traverse the skull base or for rhinoplasty.
A device developed in Russia and found in eastern European clinics called a Tonsillor is another high-energy Langevin type ultrasonic device. It is very powerful and is reported to work primarily through cavitation. It is proximately bulky and has a long, relatively thick, rigid waveguide with a variety of tips. It is used near the external surface and straight into the nasal passage as it is too large for precise intranasal work deep in the nose.